Improvement in electrokinetic remediation of heavy metal spiked kaolin with the polarity exchange technique.

In the electrokinetic treatment of heavy metal polluted soil, an alkaline environment is generated at the cathode side. It provokes the precipitation of metal ions as hydroxides into the soil and diminishes the capability of the electroremediation to clean the polluted site. In this work the "polarity exchange" technique is presented as a simple way to avoid the negative effect of OH(-) on metal transportation. This technique lies in the operation during short time intervals at inverted polarity, so that the generation of H+ ions from the oxidation of water neutralize in the alkaline zone where the metal is precipitated, favouring its dissolution. Once the metals are redissolved, the polarity is set to the original position to transport them to the desired direction. Kaolin clay contaminated with Mn was used to test the feasibility of the polarity exchange technique. The application of the "conventional technique" dealt with a removal of 14% of the initial Mn in 7.6d. For a similar treatment time the polarity exchange technique resulted in 72% of removed Mn. Successive polarity exchanges will yield with a complete decontamination of the soil with a moderate increment in the electric power consumption.